Method for preparing zeolite ssz-98

ABSTRACT

A method is disclosed for preparing zeolite SSZ-98 using 1,3-dicyclohexylimidazolium cations as a structure directing agent.

TECHNICAL FIELD

This disclosure relates generally to a method for preparing zeoliteSSZ-98 using 1,3-dicyclohexylimidazolium cations as a structuredirecting agent.

BACKGROUND

Molecular sieves are a commercially important class of crystallinematerials. They have distinct crystal structures with ordered porestructures which are demonstrated by distinct X-ray diffractionpatterns. The crystal structure defines cavities and pores which arecharacteristic of the different species.

Molecular sieves are classified by the Structure Commission of theInternational Zeolite Association (IZA) according to the rules of theIUPAC Commission on Zeolite Nomenclature. According to thisclassification, framework type zeolites and other crystallinemicroporous molecular sieves, for which a structure has beenestablished, are assigned a three letter code and are described in the“Atlas of Zeolite Framework Types,” Sixth Revised Edition, Elsevier(2007).

ERI framework type materials are characterized by three-dimensional8-membered-ring pore/channel systems containing double-six-rings (d6r)and cages. Small pore zeolites containing d6r building units and cageshave shown utility in methanol-to-olefins catalysis and in the selectivecatalytic reduction of nitrogen oxides (NO_(x))to name some of the moreimportant commercial applications.

U.S. Pat. Nos. 9,409,786 and 9,416,017 disclose an ERI framework typemolecular sieve designated SSZ-98 and its synthesis usingN,N′-dimethyl-1,4-diazabicyclo[2.2.2]octane dications as a structuredirecting agent.

It has now been found that 1,3-dicyclohexylimidazolium cations areeffective as a structure directing agent in the synthesis of SSZ-98.

SUMMARY

In one aspect, there is provided a method of preparing zeolite SSZ-98 bycontacting under crystallization conditions (1) at least one source ofsilicon oxide; (2) at least one source of aluminum oxide; (3) at leastone source of a metal selected from Groups 1 and 2 of the PeriodicTable; (4) 1,3-dicyclohexylimidazolium cations; and (5) hydroxide ions.

In one aspect, there is provided a process for preparing zeolite SSZ-98by: (a) preparing a reaction mixture containing: (1) at least one sourceof silicon oxide; (2) at least one source of aluminum oxide; (3) atleast one source of a metal selected from Groups 1 and 2 of the PeriodicTable; (4) 1,3-dicyclohexylimidazolium cations; (5) hydroxide ions; and(6) water; and (b) subjecting the reaction mixture to crystallizationconditions sufficient to form crystals of the zeolite.

In one aspect, there is provided zeolite SSZ-98 containing1,3-dicyclohexylimidazolium cations within its pore structure.

In one aspect, there is provided crystalline zeolite SSZ-98 having acomposition, as-synthesized and in the anhydrous state, in terms of moleratios, as follows:

Broad Exemplary SiO₂/Al₂O₃ 10 to 50 12 to 35 Q/SiO₂ 0.02 to 0.20 0.05 to0.20 M/SiO₂ 0.01 to 0.20 0.02 to 0.15wherein Q comprises 1,3-dicyclohexylimidazolium cations and M isselected from the group consisting of metals from Groups 1 and 2 of thePeriodic Table.

DETAILED DESCRIPTION

Introduction

The following terms will be used throughout the specification and willhave the following meanings unless otherwise indicated.

The term “zeolite” refers to crystalline aluminosilicate compositionswhich are microporous and which are formed from corner-sharing AlO₂ andSiO₂ tetrahedra.

As used herein, the numbering scheme for the Periodic Table Groups is asdisclosed in Chem. Eng. News, 63(5), 26-27 (1985).

In preparing zeolite SSZ-98, a 1,3-dicyclohexylimidazolium cation isused as a structure directing agent, also known as a crystallizationtemplate. The structure directing agent useful for making SSZ-98 isrepresented by the following structure (1):

The 1,3-dicyclohexylimidazolium cation is associated with anions whichcan be any anion that is not detrimental to the formation of thezeolite. Representative anions include elements from Group 17 of thePeriodic Table (e.g., fluoride, chloride, bromide, and iodide),hydroxide, sulfate, tetrafluoroborate, acetate, carboxylate, and thelike.

Reaction Mixture

In general, zeolite SSZ-98 is prepared by: (a) preparing a reactionmixture containing (1) at least one source of silicon oxide; (2) atleast one source of aluminum oxide; (3) at least one source of a metalselected from Groups 1 and 2 of the Periodic Table; (4)1,3-dicyclohexylimidazolium cations; (5) hydroxide ions; and (6) water;and (b) subjecting the reaction mixture to crystallization conditionssufficient to form crystals of the zeolite.

The composition of the reaction mixture from which the zeolite isformed, in terms of mole ratios, is identified in Table 1 below:

TABLE 1 Broad Exemplary SiO₂/Al₂O₃ 10 to 100 15 to 80 M/SiO₂ 0.05 to0.45 0.15 to 0.40 Q/SiO₂ 0.10 to 0.80 0.15 to 0.40 OH/SiO₂ 0.20 to 1.000.20 to 0.60 H₂O/SiO₂ 10 to 80 15 to 50wherein M is selected from the group consisting of metals from Groups 1and 2 of the Periodic Table and Q comprises 1,3-dicyclohexylimidazoliumcations.

Sources useful herein for silicon oxide include fumed silica,precipitated silicates, silica hydrogel, silicic acid, colloidal silica,tetra-alkyl orthosilicates (e.g., tetraethyl orthosilicate), and silicahydroxides.

Sources useful herein for aluminum oxide include aluminates, alumina,and aluminum compounds (e.g., aluminum chloride, aluminum hydroxide, andaluminum sulfate), kaolin clays, and other zeolites (e.g., zeolite Y).

As described herein above, for each embodiment described herein, thereaction mixture can be formed using at least one source of a metal (M)selected from Groups 1 and 2 of the Periodic Table. In onesub-embodiment, the reaction mixture is formed using a source of a metalfrom Group 1 of the Periodic Table. In another sub-embodiment, thereaction mixture is formed using a source of potassium (K). AnyM-containing compound which is not detrimental to the crystallizationprocess is suitable. Sources for such Groups 1 and 2 metals includeoxides, hydroxides, nitrates, sulfates, halides, acetates, oxalates andcitrates thereof.

Optionally, the reaction mixture may contain seed crystals. In oneembodiment, synthesis of the crystalline zeolite is facilitated by thepresence of 0.05 to 10.0 wt. % (e.g., 1 to 5 wt. %) seed crystals basedon the total weight of the reaction mixture. The seed crystals can beisostructural with the desired zeolite, for example, the product of aprevious synthesis.

For each embodiment described herein, the reaction mixture can besupplied by more than one source. Also, two or more reaction componentscan be provided by one source.

The reaction mixture can be prepared either batch wise or continuously.Crystal size, morphology and crystallization time of the crystallinezeolite described herein can vary with the nature of the reactionmixture and the crystallization conditions.

Crystallization and Post-Synthesis Treatment

Crystallization of the zeolite can be carried out under either static,tumbled or stirred conditions in a suitable reactor vessel, such as forexample polypropylene jars or Teflon-lined or stainless steelautoclaves, at a temperature of from 125° C. to 200° C. for a timesufficient for crystallization to occur at the temperature used, e.g.,from 1 day to 14 days.

Once the zeolite crystals have formed, the solid product is separatedfrom the reaction mixture by standard mechanical separation techniquessuch as centrifugation or filtration. The crystals are water-washed andthen dried to obtain the as-synthesized zeolite crystals. The dryingstep is typically performed at a temperature of less than 200° C.

As a result of the crystallization process, the recovered crystallinezeolite product contains within its pore structure at least a portion ofthe structure directing agent used in the synthesis.

The structure directing agent is typically at least partially removedfrom the zeolite by calcination before use. Calcination consistsessentially of heating the zeolite comprising the structure directingagent at a temperature of from 200° C. to 800° C. in the presence of anoxygen-containing gas, optionally in the presence of steam. Thestructure directing agent can also be removed by photolysis techniquesas described in U.S. Pat. No. 6,960,327.

To the extent desired and depending on the composition of the zeolite,any cations in the as-synthesized or calcined zeolite can be replaced inaccordance with techniques well known in the art by ion exchange withother cations. Preferred replacing cations include metal ions, hydrogenions, hydrogen precursor, e.g., ammonium ions and mixtures thereof.Particularly preferred cations are those which tailor the catalyticactivity for certain hydrocarbon conversion reactions. These includehydrogen, rare earth metals and metals of Groups 2 to 15 of the PeriodicTable of the Elements. As used herein, the term “as-synthesized” refersto the zeolite in its form after crystallization, prior to removal ofthe SDA cation.

The zeolite disclosed herein can be formulated with into a catalystcomposition by combination with other materials, such as binders and/ormatrix materials, which provide additional hardness or catalyticactivity to the finished catalyst.

Characterization of the Zeolite

SSZ-98 zeolites made by the process disclosed herein have a composition(in terms of mole ratios), as-synthesized and in the anhydrous state, asdescribed in Table 2 below:

TABLE 2 Broad Exemplary SiO₂/Al₂O₃ 10 to 50 12 to 35 Q/SiO₂ 0.02 to 0.200.05 to 0.20 M/SiO₂ 0.01 to 0.20 0.02 to 0.15wherein Q comprises 1,3-dicyclohexylimidazolium cations and M isselected from the group consisting of metals from Groups 1 and 2 of thePeriodic Table.

It should be noted that the as-synthesized form of the SSZ-98 zeolitemay have molar ratios different from the molar ratios of reactants ofthe reaction mixture used to prepare the as-synthesized form. Thisresult may occur due to incomplete incorporation of 100% of thereactants of the reaction mixture into the crystals formed (from thereaction mixture).

SSZ-98 is characterized by an X-ray diffraction pattern which, in theas-synthesized form of the zeolite, includes at least the lines set outin Table 3 below.

TABLE 3 Characteristic Peaks for As-Synthesized SSZ-98 2-Theta^((a))d-spacing (nm) Relative Intensity^((b)) 7.78 1.136 VS 9.74 0.907 W 11.790.750 W 13.46 0.657 S 14.10 0.627 W 15.53 0.570 M 16.62 0.533 W 19.510.455 W 20.56 0.432 VS 21.40 0.415 M 23.38 0.380 S 23.76 0.374 VS 24.880.358 W ^((a))±0.20 ^((b))The powder XRD patterns provided are based ona relative intensity scale in which the strongest line in the X-raydiffraction pattern is assigned a value of 100: W = weak (>0 to ≦20); M= medium (>20 to ≦40); S = strong (>40 to ≦60); VS = very strong (>60 to≦100).

In its calcined form, the aluminosilicate SSZ-98 zeolite disclosedherein has a composition comprising the molar relationship:

Al₂O₃:(n)SiO₂

wherein n has a value of from 10 to 50 (e.g., from 10 to 35, from 10 to25, from 10 to 20, from 10 to 15, from 12 to 50, from 12 to 35, from 12to 25, from 12 to 20, from 15 to 50, or from 15 to 35).

SSZ-98 is characterized by an X-ray diffraction pattern which, in thecalcined form of the zeolite, includes at least the lines set out inTable 4.

TABLE 4 Characteristic Peaks for Calcined SSZ-98 2-Theta^((a)) d-spacing(nm) Relative Intensity^((b)) 7.76 1.138 VS 9.78 0.904 W 11.79 0.750 W13.45 0.658 VS 14.07 0.629 W 15.51 0.571 W 16.61 0.533 W 19.50 0.455 W20.54 0.432 S 21.39 0.415 W 23.37 0.380 M 23.73 0.375 S 24.92 0.357 W^((a))±0.20 ^((b))The powder XRD patterns provided are based on arelative intensity scale in which the strongest line in the X-raydiffraction pattern is assigned a value of 100: W = weak (>0 to ≦20); M= medium (>20 to ≦40); S = strong (>40 to ≦60); VS = very strong (>60 to≦100).

Minor variations in the diffraction pattern can result from variationsin the mole ratios of the framework species of the particular sample dueto changes in lattice constants. In addition, sufficiently smallcrystals will affect the shape and intensity of peaks, leading tosignificant peak broadening. Minor variations in the diffraction patterncan result from variations in the organic compound used in thepreparation. Calcination can also cause minor shifts in the X-raydiffraction pattern. Notwithstanding these minor pertubations, the basiccrystal structure remains unchanged.

The powder X-ray diffraction patterns presented herein were collected bystandard techniques. The radiation was CuK₊ radiation. The peak heightsand the positions, as a function of 2θ where θ is the Bragg angle, wereread from the relative intensities of the peaks, and d, the interplanarspacing corresponding to the recorded lines, can be calculated.

In one embodiment, zeolite SSZ-98 prepared in accordance with thisdisclosure is preferably substantially free of non-ERI framework typematerial. By “substantially free of non-ERI framework type material” ismeant that the zeolite composition disclosed herein contains less than2.5% non-ERI framework type character (e.g., less than 1% non-ERIframework type character, less than 0.5% non-ERI framework typecharacter, or no measurable non-ERI framework type character), asmeasured by X-ray diffraction. The presence of these impurities can bedetermined and quantified by analysis of the X-ray diffraction patternof a sample. The term “non-ERI framework type material” used hereinmeans any material that does not contain crystalline zeolite of the ERIframework type. Examples of such non-ERI framework type materialinclude, for example, amorphous material and OFF framework typezeolites.

SSZ-98 has either a rod-like crystal morphology or a plate crystalmorphology.

EXAMPLES

The following illustrative examples are intended to be non-limiting.

Example 1

0.78 g of 45% KOH solution and 1.00 g of CBV720 Y zeolite (ZeolystInternational, SiO₂/Al₂O₃ mole ratio=30) were mixed together in a Teflonliner. Then, 5.86 g of 10% 1,3-dicyclohexylimidazolium hydroxidesolution (SACHEM Inc.) was added to the mixture. The resulting gel wasstirred until it became homogeneous. The liner was capped and placedwithin a Parr steel autoclave reactor. The autoclave was placed in anoven and heated at 135° C. for 5 days. The solid products were recoveredfrom the cooled reactor by centrifugation, washed with deionized waterand dried at 95° C.

The resulting product was identified by powder XRD and SEM to be pureSSZ-98 zeolite.

The product had a SiO₂/Al₂O₃ mole ratio of 12.2, as determined by ICPelemental analysis.

Example 2

1.61 g of 45% KOH solution and 2.00 g of CBV760 Y-zeolite (ZeolystInternational, SiO₂/Al₂O₃ mole ratio=60) were mixed together in a Teflonliner. Then, 20.17 g of 10% 1,3-dicyclohexylimidazolium hydroxidesolution (SACHEM Inc.) was added to the mixture. The resulting gel wasstirred until it became homogeneous. The liner was capped and placedwithin a Parr steel autoclave reactor. The autoclave was placed in anoven and heated at 135° C. for 6 days. The solid products were recoveredfrom the cooled reactor by centrifugation, washed with deionized waterand dried at 95° C.

The resulting product was identified by powder XRD and SEM to be pureSSZ-98 zeolite.

The product had a SiO₂/Al₂O₃ mole ratio of 14.5, as determined by ICPelemental analysis.

Example 3

1.81 g of 45% KOH solution and 2.00 g of CBV780 Y-zeolite (ZeolystInternational, SiO₂/Al₂O₃ mole ratio=80) were mixed together in a Teflonliner. Then, 12.10 g of 10% 1,3-dicyclohexylimidazolium hydroxidesolution (SACHEM Inc.) was added to the mixture. The resulting gel wasstirred until it became homogeneous. The liner was capped and placedwithin a Parr steel autoclave reactor. The autoclave was placed in anoven and heated at 135° C. for 6 days. The solid products were recoveredfrom the cooled reactor by centrifugation, washed with deionized waterand dried at 95° C.

The resulting product was identified by powder XRD and SEM to be pureSSZ-98 zeolite.

The product had a SiO₂/Al₂O₃ mole ratio of 15.2, as determined by ICPelemental analysis.

As used herein, the term “comprising” means including elements or stepsthat are identified following that term, but any such elements or stepsare not exhaustive, and an embodiment can include other elements orsteps.

Unless otherwise specified, the recitation of a genus of elements,materials or other components, from which an individual component ormixture of components can be selected, is intended to include allpossible sub-generic combinations of the listed components and mixturesthereof.

All documents cited in this application are herein incorporated byreference in their entirety to the extent such disclosure is notinconsistent with this text.

1. A method of preparing zeolite SSZ-98, comprising: (a) preparing areaction mixture containing: (1) at least one source of silicon oxide;(2) at least one source of aluminum oxide; (3) at least one source of ametal (M) selected from Groups 1 and 2 of the Periodic Table; (4)1,3-dicyclohexylimidazolium cations (Q); (5) hydroxide ions; and (6)water; and (b) subjecting the reaction mixture to crystallizationcondition sufficient to form crystals of the zeolite.
 2. The method ofclaim 1, wherein the zeolite is prepared from a reaction mixturecomprising, in terms of mole ratios, the following: SiO₂/Al₂O₃ 10 to 100M/SiO₂ 0.05 to 0.45 Q/SiO₂ 0.10 to 0.80 OH/SiO₂ 0.20 to 1.00 H₂O/SiO₂ 10to
 80.


3. The method of claim 1, wherein the zeolite is prepared from areaction comprising, in terms of mole ratios, the following: SiO₂/Al₂O₃15 to 80 M/SiO₂ 0.15 to 0.40 Q/SiO₂ 0.15 to 0.40 OH/SiO₂ 0.20 to 0.60H₂O/SiO₂ 15 to
 50.


4. The method of claim 1, wherein the zeolite has a composition,as-synthesized and in the anhydrous state, in terms of mole ratios, asfollows: SiO₂/Al₂O₃ 10 to 50 Q/SiO₂ 0.02 to 0.20 M/SiO₂ 0.01 to 0.20.


5. The method of claim 1, wherein the zeolite has a composition,as-synthesized and in the anhydrous state, in terms of mole ratios, asfollows: SiO₂/Al₂O₃ 12 to 35 Q/SiO₂ 0.05 to 0.20 M/SiO₂ 0.02 to 0.15.


6. The method of claim 1, wherein the zeolite has, in its as-synthesizedform, an X-ray diffraction pattern including the following lines:2-Theta d-spacing (nm) Relative Intensity  7.78 ± 0.20 1.136 VS  9.74 ±0.20 0.907 W 11.79 ± 0.20 0.750 W 13.46 ± 0.20 0.657 S 14.10 ± 0.200.627 W 15.53 ± 0.20 0.570 M 16.62 ± 0.20 0.533 W 19.51 ± 0.20 0.455 W20.56 ± 0.20 0.432 VS 21.40 ± 0.20 0.415 M 23.38 ± 0.20 0.380 S 23.76 ±0.20 0.374 VS 24.88 ± 0.20 0.358 W.


7. An SSZ-98 zeolite comprising 1,3-dicyclohexylimidazolium cationswithin in its pore structure.
 8. The zeolite of claim 7, wherein thezeolite has a SiO₂/Al₂O₃ mole ratio of from 10 to
 50. 9. The zeolite ofclaim 7, wherein the zeolite has a SiO₂/Al₂O₃ mole ratio of from 12 to35.
 10. The zeolite of claim 7, having, in its as-synthesized form, anX-ray diffraction pattern including the following lines: 2-Thetad-spacing (nm) Relative Intensity  7.78 ± 0.20 1.136 VS  9.74 ± 0.200.907 W 11.79 ± 0.20 0.750 W 13.46 ± 0.20 0.657 S 14.10 ± 0.20 0.627 W15.53 ± 0.20 0.570 M 16.62 ± 0.20 0.533 W 19.51 ± 0.20 0.455 W 20.56 ±0.20 0.432 VS 21.40 ± 0.20 0.415 M 23.38 ± 0.20 0.380 S 23.76 ± 0.200.374 VS 24.88 ± 0.20 0.358 W.